Thread: spun bearings

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Spun mains twice, corrected oiling problem with oil cooler. Now spinning rods, twice so far. Its not mine, pretty sure its built right, all new parts, turned crank after first spin. last time it spun though in just a couple of half as.. passes. BUT his boost gauge pegged out at 25 and the car stood up off the line,which it never does. So can too much boost pressure overcome oil pressure causing bearings to contact crank and spin or should he look to other problems...........350 sbc 2xturbos...............6500rpm rev chip.

25 is all the gauge had on it, I would guess it was 30 or better. I am not sure what his oil pressure is. Even if it had good oil pressure I was just thinking that much boost would be too much. As far as clearances, well that prob wasn't checked. If you have a 10-10 crank and a 10 bearing do you still need to check clearance? I havn't ever checked clearances on anything I have built, but never built anything much over stock.
Thats another story all together too, I am building a 327, crank turned 10-10 with 10 bearings, guess I should use that plastigauge they sent me, but what do I do if it is off? everything has already been turned balanced and put together. Pardon my inexperience on these details, all we every did was put it together and run the heck out of it.

I've seen so many mistakes made at machine shops, I mic everything before it goes together. With a twin turbo engine, the entire assembly should be blueprinted, that's one heck of a load to be putting on any kind of bottom end. I'm also a bit curious what rods you are using? Spun rod bearings to me would indicate either an oiling problem or some egg shaped rod big ends....

Originally Posted by Dave Severson

I've seen so many mistakes made at machine shops, I mic everything before it goes together. With a twin turbo engine, the entire assembly should be blueprinted, that's one heck of a load to be putting on any kind of bottom end. I'm also a bit curious what rods you are using? Spun rod bearings to me would indicate either an oiling problem or some egg shaped rod big ends....

Like Dave said here about the rods.
You must also make sure you have plenty of side to side clearance with the rods.
If the rods egg shape or pinch this will cause oil starvation.
Over 25 lbs. of boost???

Don't ever assume anything. I just took a motor down today that has only a couple hundred miles on it with all the rod bearings spun. They didn't flatten out, just rolled in the rods. Turns out the builder used standard bearings on a .010" under crank. The mains are standard though.


BTW, that boost shouldn't tear the bearings up. Will be rough on other parts though no doubt.
Detonation will though.

Originally Posted by camaro_fever68

Detonation will though.

My moneys on detonation. When I first started with sbc, everyone told me 38-39 degrees total advance ignition timing even though I was working on a 400. Well I spun more bearings than you could imagine and this is without power adders. Once I figured out that more stroke equates to more compression during the same 38-39 degrees of rotation, the problem was solved. Now I only run 34 degrees total and when I hit nos, I drop another 4 degrees for every one hundred hp.

Sooooo, if you were running 25 plus boost, that has got to equate to some 3-500 hp which means the timing should have been compensated for by up to 20 degrees less.

What timing and what fuel were you using?

Originally Posted by TyphoonZR

My moneys on detonation. When I first started with sbc, everyone told me 38-39 degrees total advance ignition timing even though I was working on a 400. Well I spun more bearings than you could imagine and this is without power adders. Once I figured out that more stroke equates to more compression during the same 38-39 degrees of rotation, the problem was solved. Now I only run 34 degrees total and when I hit nos, I drop another 4 degrees for every one hundred hp.

Sooooo, if you were running 25 plus boost, that has got to equate to some 3-500 hp which means the timing should have been compensated for by up to 20 degrees less.

What timing and what fuel were you using?

This could be very possible.
I would really like to see a twin turbo 350 that has 25+ lbs. of boost.

Originally Posted by erik erikson

This could be very possible.
I would really like to see a twin turbo 350 that has 25+ lbs. of boost.

you think

Originally Posted by pat mccarthy

you think

Pat are you thinking what I am thinking???

Good thread.

you need to run then bearings LOOSE .003 +on them rods and you need to run a H bearing you can not just put the crank in with .010 bearing and call it good way to many sizes on rod bore and the crank they all have a hi / low size and on bearings they can very so much i will not get in to it NO way would i ever think of not checking oil clearances i check all oil clearance on engines i do stock and race

Banks sells a kit that is capable of 30psi. That would translate into over 1500hp out of a 350 if done right. I've been considering an LS build with one for some time. Motown 4.125 block, 4.0" stroke, AFR heads, C'mon lotto numbers.......

do you have it set to retard the timing when you start boosting.... if not you could be getting detonation which is hard on everything in the motor... also always always always check clearances.... so many factors... theres no perfect machining on anything, its close... really close but not perfect... then theres your torque wrench it could be a little off on torque.... and can get more and more off depending what depth socket and extension you're using....then there can be things such as bolt threads that can throw torque off.... that plastigauge stuff is one of the cheapest securities when building your motor...

i did some work on a buick v6 that made 25 all the best parts are needed and someone that knows how the build and tune did a 540 twin turbo still looking for the dyno numbers on that one i really do not think he will push it to 25 ?but did use some nice parts

the timming weights are removed and welded up at full advance. Runs 118 octane and normally 8 to 10 psi. he didn't want to run over 25 psi boost but the gates stuck and it boosted that high. car normally is mid 9 secs, when it over boosted it did two wheel stands in the first 60 ft then coasted to a 13 second 1/4. Spun all the bearings in that one run. The crank had just been turned and the machine shop checked all the rods and replaced 2 of them.